A battery module (electric storage apparatus) described in JP-A-2000-348781 is conventionally known. The battery module is formed by arranging a plurality of cells (electric storage devices) to be electrically connected. The cell is formed by housing a power generating element in a case.
Heat is generated from the power generating element when the cell charges or discharges. The heat accumulates in the cell, and it is feared that the performance of the battery decreases if the temperature of the cell increases. Moreover, in the case of an assembled battery, it is feared that temperature variations in cells are caused by heat generation, and variations in the degrees of the decrease in battery performance are caused, too.
Hence, in the conventional technology, a cooling device for cooling a cell is placed on the exterior of the case. A coolant is circulated in the cooling device. An outer surface of the case is in contact with the cooling device; accordingly, heat generated in the power generating element upon charge or discharge is transferred to the cooling device through the case. Accordingly, the temperature inside the case decreases, so that the battery performance is inhibited from decreasing.
However, it is feared that the power generating element expands upon charge. Accordingly, it is feared that in an area where the power generating element is in contact with an inner surface of the case, the case is pressed and expanded by the expanded power generating element.
If the case expands, it is feared that a gap is formed between the expanded case and the cooling device. The gap includes an air layer. Since thermal conductivity is relatively low in the air layer, it is feared that heat is not sufficiently transferred from the case to the cooling device in the area where the gap is formed between the cooling device and the case. Consequently, it is feared that the temperature of the cell becomes high locally.
Especially when charge and discharge are repeated, the case repeats expansion and contraction. Accordingly, it becomes easy for a gap to be formed between the case and the cooling device, so that the need to cool the cell evenly is high.